Many devices, including most hand-held wireless devices, use one or more batteries as the electric power source. One popular type of battery that is used is a lithium battery, such as a lithium thionyl chloride battery, due to its relatively high energy density and low self-discharge rate. The low self-discharge rate allows lithium batteries to exhibit a longer shelf life as compared to various other battery types.
The main reason that lithium batteries have such a low self-discharge is that a protective layer is formed on these batteries during periods of non-use (e.g., storage). This protective layer begins forming during the manufacturing process, as soon as the electrolyte comes into contact with the lithium anode. The protective layer consists of lithium chloride crystals, and as it grows it prevents further reaction. This protective layer formation phenomenon is generally referred to as “passivation,” and is most significantly observed when freshly manufactured batteries are stored for an extended period of time, such as 3 months or more. The protective layer formation can also be accelerated by environmental factors.
Although passivation is responsible for the relatively low self-discharge rate of lithium batteries, it also causes certain drawbacks. For example, passivation may also increase the internal resistance of the battery. This increased internal resistance may cause the battery to not respond to peak pulse current requirements for certain functions, such as wireless transmission. This can, in some instances, render the product unusable.
It is generally known that applying a current drain to a lithium battery will breakdown the protective layer. During a current drain, lithium ion movement is increased, which disturbs the ionic lattice of the protective layer, eventually breaking it down. This process is called “depassivation.” The challenge in depassivation is to not load the battery, while effectively depassivating it. Presently known methods thus rely on separate depassivation devices that require removal of the batteries from the end-use device and/or various other costly and/or labor intensive methods.
Hence, there is a need for a system and method of depassivating a lithium battery that does not rely on separate depassivation devices and/or removal of the batteries from the end-use device and/or that is not costly and/or labor intensive. The present invention addresses one or more of these needs.